It iw well known that after a silver halide photographic light-sensitive material is exposed to light, an oxidized aromatic primary amine developing agent reacts with a dye forming coupler to form color images. In this type of process, color reproduction by a conventional substractive process is used to form color images composed of cyan, magenta, and yellow dyes, which are the complementary colors of red, green, and blue, respectively. The reaction of the coupler with the oxidation product of the color developing agent is carried out at a coupling active site. A coupler having a hydrogen atom as a substituent at the active site is known as a 4-equivalent coupler, i.e., a coupler which stoichiometrically requires 4 mols of silver halide having a development nucleus as an oxidizing agent for forming 1 mol of dye.
On the other hand, a coupler having a group releasable as an anion as a substituent at the active site is known as a 2-equivalent coupler, i.e., a coupler which requires only 2 mols of silver halide having a development nucleus for forming 1 mol of dye. Accordingly, the processing time for photographic light-sensitive materials can be shortened, and the sharpness of the color images formed can be improved when a 2-equivalent coupler is used, as compared with using a 4-equivalent coupler, because it is possible to reduce the amount of silver halide in the light-sensitive layer of the photographic material and thus reduce the thickness of the layer. Further, in 2-equivalent couplers, it is possible to change the coupling activity with respect to the color developing agent by changing the properties of the releasing group.
Several attempts have been made for the purpose of preparing 2-equivalent couplers from 5-pyrazolone type couplers which are employed very often in practice. For instance, the 4-position of the pyrazolone ring can be substituted with a thiocyano group as described in U.S. Pat. Nos. 3,214,437 and 3,253,924, an aryloxy group as described in U.S. Pat. No. 3,419,391, a 2-triazolyl group as described in U.S. Pat. No. 3,617,291, or a halogen atom as described in U.S. Pat. No. 3,522,052.
However, these 4-position substituted pyrazolone couplers have several disadvantages in that they cause the formation of severe color fog, in that they have a relatively low coupling activity, in that they are chemically unstable per se and liable to convert into compounds which are unable to form color with the lapse of time and in that they are difficult to synthesize, etc.
Further, U.S. Pat. Nos. 3,227,554, 4,366,237 and 4,522,915, etc. describe that the 4-position of pyrazolone may be substituted with an alkylthio group, an arylthio group or a heterocyclic thio group. However, these couplers are also disadvantageous since they also have a relatively low coupling activity, or their properties are liable to deteriorate in photographic light-sensitive materials during preservation, etc.
On the other hand, in U.S. Pat. No. 3,700,454, it is described that an alkyl-substituted phenoxyalkyl carboxylic acid is employed as a solvent component for a coupler having an alkyl-substituted phenoxyalkanamido group as a diffusion resistant group. However, there is no description relating to the magenta couplers used in the present invention in this patent. Further, in the present invention it is not necessary that the coupler comprise the alkyl-substituted phenoxyalkanamido group as described in the above-described patent and that the carboxylic acid compound is the alkyl-substituted phenoxyalkyl carboxylic acid.
Moreover, improvements in color forming property and graininess achieved by a carboxylic acid type compound having an ester group are described in U.S. Pat. No. 4,464,464. However, the remarkable effects according to the present invention are peculiarly exhibited only when these (or other) carboxylic acid type compounds are used in combination with the magenta couplers according to the present invention. Further, carboxylic acid compounds outside the scope of the above-noted U.S. patent are also effective in the present invention.